Digital printing is often achieved using a single spatial light modulator, such as a low cost liquid crystal display (LCD) modulator, to expose photographic paper. Several photographic printers using commonly available LCD technology are described in U.S. Pat. Nos. 5,652,661; 5,701,185; and 5,745,156. Most of these designs involve the use of a transmissive LCD modulator such as is depicted in U.S. Pat. Nos. 5,652,661 and 5,701,185.
A problem with all of these devices is that they occasionally produced defects in the final image. These defects may be due to, for example, surface finishing of the LCD, which results in high spatial frequency defects. Another defect, again using the LCD as an example, is low spatial frequency defects in the resulting image caused by warping of the support plate as it is attached to the LCD during manufacture.
In copending U.S. patent application Ser. No. 09/606,891 correction for such spatial defects is described, and provides for a simple means to correct such defects using a correction defect map, along with a gain correction table. In copending U.S. patent application Ser. No. 09/712,641 a means for adequately generating the correction defect map is provided. U.S. patent application Ser. No. 09/712,641 addresses the issue of providing adequate registration and a correction map for high spatial frequency defects. However, the gain correction table used by U.S. patent application Ser. No. 09/606,891 is determined in a subjective manner using photographic prints and human judgement.
It is a purpose of this invention to provide means for creating a correction gain table in a non-subjective, timely, and manufacturable way.